Work Step by Step
$Area=120=1/2 \times bh$ $b=3h+6$ $120=1/2 \times (3h+6)(h)$ $240=3h^2+6h$ $3h^2+6h-240=0$ $h^2+2h-80=0$ $(h+10)(h-8)=0$ $h=-10,8$ $h=8$, because height cannot be negative
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